1.1. Field of the Invention
The present invention relates to the field of computer technology, and in particular to a method and system for compressing digital data from a row-column structured, multi-color bitmap image representation and to advantageous thereof for low bandwidth data communication.
1.2. Description and Disadvantages of Prior Art
A prior art compression scheme is published in a scanner handbook of CHINON INDUSTRIES, INC., “IMAGE SCANNER”, TECHNICAL REFERENCE MANUAL, N-207, DS-3000, published by SHENON INDUSTRIES in 1988 and available from SHENON AMERICA, INC. INFORMATION EQUIPMENT DIFF., 660 MAPLE AVENUE, TORRANCE, CA 90503 U.S.A.
In order to provide for an effective, two-dimensional data compression scheme it is proposed in this prior art method to generally reduce the data volume and respective transmission time volume by the following basic compression scheme: The data in one line is divided into 8 bits. When all 8 bits are “0”, they will be skipped. Otherwise, the 8 bits will be transmitted as compression coding “1”. If the maximum data of for example 316 bytes in one line is coded, the data is expressed by the compression codes of 40 bytes, whereby the least significant 4 bits of the last byte has no meaning. If the compression codes of 40 bytes are compressed two more times the codes are compressed to 1 byte. In other words, a byte having one or more “1” bits is mapped to a bit value of “1”, and the byte is stored in a retrievable manner, preferred directly behind said compressed string and a byte only consisting of “0” bits is mapped to a “0” bit value. In order to adapt this basic compression method to the above-mentioned two-dimensional image representations this prior art publication proposes a bit-wise EXCLUSIVE OR (X-OR) operation between respective bits or pixels of subsequent rows in a row-column structured bitmap representation. That means when previous row-bits or pixels in the same column position are identical, then a “0” is the X-OR result, whereas if the two bits are different, then a “1” is the X-OR operation result. The X-OR operation is done line-wise (row-wise) before the execution of the before-mentioned one-dimensional data compression).
A disadvantage of this prior art compressing method is that it is not efficient enough for compressing image representations, which occur typically in GUI-oriented program applications and handles only black and white pictures.
According to a second aspect of the present invention such compressed data is frequently communicated via networks, either having lower or larger bandwidths. For example, when using an Intranet and browsing some portal, much transmission time is spent for transmitting the large amount of data needed for the end-user to see a multicoloured, high resolution graphic at his terminal device. In particular, if said device is coupled via a low bandwidth line, this takes an intolerable time until a user sees a GUI-structured screen at his terminal device. Having for example a transmission rate of 9.6 Kbits per second, the transmission time for a portal screen may be roughly six minutes.
Also for remote application control between such low bandwidth-coupled, maybe handheld terminal device and a backend application server the same problem exists.
1.3. Objectives of the Invention
It is thus an objective of the present invention to provide an improved compressing method and its advantageous use for networked applications.